There are many applications in which electronic components, devices and the like have a variety of parts including "leads," contacts and similar connecting elements which are plated with a thin layer of gold (about 50 microinches or even more) to enhance the electrical quality and environmental resistance of the circuits involved. Electrical quality and reliability of the various elements and/or components in the circuits play a major role in the suitability thereof and of the devices and systems in which they are employed. Quality and reliability frequently depend on the type of connecting elements used and the means used to join them.
Soldering is a widely used technique for readily joining elements of electrical circuits in both mass production and hand assembly operations. The structure and composition of the elements, such as the "leads," to be joined as well as the type, size and mode of operation of the circuit and components thereof are factors in determining the suitability of known soldering techniques and materials. For example, the strength and reliability of the joint frequently depends on both the composition of the elements to be joined and of the joining material such as the solder; the type and/or size of elements in an electronic component must be considered when establishing the time and temperatures that can be employed in the joining operation; service conditions and accessibility relate to the materials and temperatures required for the joining techniques and suitability thereof in mass production operations.
A widely used soldering technique for electronic components employs tin-containing solder whereby joining can be carried out rapidly at relatively low temperatures, e.g. about 400.degree. F. However, as is known, joining with a tin-containing solder to surfaces over which even a flash coating (about 10 to 30 microinches) of gold has been applied results in embrittlement and ultimate failure of the gold-tin solder joint over a period of time by virtue of the interaction of the gold and tin. Thus, the strength, time and temperature advantages of this type of joining technique are not readily available for a large number of electronic components where gold plating of the surfaces is required.
Numerous attempts have been made over the years to overcome the problem of soldering to gold plated surfaces, but to date no routine or economically feasible procedures and/or solder materials have been developed which afford the strength, reliability and other advantages of basic tin-containing solders. Moreover, in those cases where the use of high temperatures would be detrimental to the electronic components or substrates, it has been necessary to employ complicated and costly mechanical or chemical procedures for joining to those surfaces which are required to be gold plated. For example, one such procedure involves masking portions of the part before gold plating to limit the coating to areas where joining to the surface would not be needed. Masking and then removal of the masking before assembly and related operations greatly increase the complexity and costs, particularly when mass production of large quantities of small parts is involved.
Mechanical abrading, reforming, compacting and cleaning of articles made of metals, ceramics, refractory materials or plastics by "sand-blasting" and analogous high velocity impacting treatment procedures are well known and widely used. This manner for treatment of generally hard surfaces typically involves bombardment of them with fine grains of abrasive materials at high velocity utilizing a jet of compressed air or other suitable fluid. While the term "sandblasting" has generally attained a generic meaning for treating the surfaces of articles by high velocity impacting with granular or particulate abrasive materials, the treatments used involve a wide range of different apparatus and procedures as well as many different types, sizes and shapes of abrasive materials depending on the application, such as the type and composition of the materials being treated, and the purpose of the treatment.
Quartz sand used for blasting parts in the past with the aid of compressed air, in general, has been found to be unsuitable for environmental reasons as well as being subject to premature breaking when impacting metal surfaces In U.S. Pat. Nos. 2,145,756, 2,336,001, 2,362,310, 2,600,358, 2,670,281, 2,773,339, 2,796,338, 3,188,776, 4,035,962, 4,289,541 and Re. No. 31,883 are disclosed examples of some of the many metallic materials used as particulate abrasives for "sand blasting" and grinding treatment of the surfaces of metal articles including slabs, sheets and castings. None of these patents deal with the problem of joining to surfaces to be or that have been gold plated, or to apparatus for the preparation of parts used in electronic components.
More recently, "sand blasting" and analogous techniques have been used for a variety of non-metal treating applications including, for example, removing insulation from insulated wires as disclosed in U.S. Pat. No. 3,636,623, and as a finishing step for plastic parts such as removing flash or excess material from molded parts including electronic components as disclosed in U.S. Pat. Nos. 4,545,155, 4,555,876 and 4,561,219. In such applications, special apparatus and fixtures are used for controlling the area treated with various different types of abrasive materials, typically of special composition, size and shape. Here again, the problem of joining to gold plated surfaces is not dealt with, nor is there a suggestion of any method which may be suitable, although the treatment of substrate surfaces to be coated and the finishing of coated surfaces of electronic components are disclosed.